As a liquid crystal display device employing a liquid crystal material, a TN (twisted nematic) mode liquid crystal display device is in practical use. In such a mode, light switching is carried out by utilizing the optical rotation property of a liquid crystal, and a liquid crystal display device in this mode requires use of a polarizing plate. However, use of a polarizing plate lowers light utilization efficiency.
As a liquid crystal display device which achieves high light utilization efficiency without using a polarizing plate, a liquid crystal display device in which switching is conducted between a transmission state (also called a transparent state) and a scattering state of a liquid crystal may be mentioned, and a liquid crystal display device employing a polymer dispersed liquid crystal (PDLC) or a polymer network liquid crystal (PNLC) is commonly known.
A liquid crystal display device employing such a liquid crystal is a liquid crystal display device having a liquid crystal layer between a pair of substrates provided with electrodes, formed by disposing a liquid crystal composition containing a polymerizable compound which undergoes polymerization by ultraviolet rays between the pair of substrates and curing the liquid crystal composition by irradiation with ultraviolet rays, to form the liquid crystal layer, that is, a cured product composite (for example, a polymer network) of the liquid crystal and the polymerizable compound. In such a liquid crystal display device, the transmission state and the scattering state of the liquid crystal are controlled by application of a voltage.
A conventional liquid crystal display device employing PDLC or PNLC is a liquid crystal display device (also called a normal device) which is in a cloudy (scattering) state when no voltage is applied, since liquid crystal molecules are randomly aligned, and is in a transmission state when a voltage is applied, since liquid crystal molecules are aligned in an electric field direction, whereby light is transmitted. However, in a normal device, it is necessary to always apply a voltage in order to obtain a transmission state, and accordingly when it is used for an application which is mainly used in a transparent state, for example, when used for window glass, the electrical power consumption tends to be large.
On the other hand, a liquid crystal display device employing PDLC (also called a reverse device), which is in a transmission state when no voltage is applied and is in a scattering state when a voltage is applied, has been reported (Patent Documents 1 and 2).